Used one for years on 2 different shifters. Works fine. It does switch ground on either the yellow or gray wire. Yellow is normally open, gray is normally closed. A shifter solenoid will typically use the yellow wire to provide ground at the set RPM necessitating the solenoid to have one wire hot with the other being the switched ground. Never used a relay, never saw the need just to run that little solenoid for a split second.
Use a playback tach or data recorder to verify the shift point. MSD chips aren't perfect, electronics lag, shift linkage has to move and the trans has to do it's thing.
Last edited by CMcAllister; 05/06/19 01:21 PM.